Bjorndal et al.: Estimates of survival for Caretta caretta in the North Atlantic 



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tal capture in longline fisheries in the Azores does increase 

 with size, with the 2 to 6 year age classes experiencing very 

 little mortahty (Bolten,in press). Thus, if our estimate ofS 

 (calculated for the age classes between threshold age and 

 age 6) were applied to the entire oceanic stage, the effect 

 of mortality in longline fisheries, or other fisheries biased 

 to large size classes, would be underestimated. 



The estimate of 0.911 for annual survival probabilities 

 for oceanic-stage loggerhead sea turtles in the waters of 

 the Azores indicates high survival in this lifestage without 

 mortality from longline fisheries. Species characterized by 

 long life and late sexual maturity, such as loggerhead sea 

 turtles, require very high survival throughout immature 

 stages to maintain populations (Congdon et al., 1993; 

 Grouse, 1999). This high probability of survival is also 

 consistent with the theory that lower predation in oceanic 

 habitats compared to neritic habitats is the selective pres- 

 sure that maintains oceanic juvenile stages in most species 

 of sea turtles (Bolten, 2003). 



In two updated matrix models for North Atlantic log- 

 gerhead sea turtles (that differed in stage lengths). Hep- 

 pell et al. (in press) derived fitted estimates of 0.745 and 

 0.875 for annual survival probabilities of the oceanic stage, 

 which they defined as spanning 5 to 45 cm carapace length. 

 Chaloupka (in press) derived an estimate of annual sur- 

 vival probability for oceanic-stage loggerhead sea turtles 

 in Australia of 0.67 sampled from a logistic probability 

 density function that ranged from 0.60 to 0.76 and had 

 a mode at 0.67. The tuned estimate of 0.67 was derived 

 from a stochastic simulation model that incorporated em- 

 pirically based survival probability estimates for all age 

 classes in the model except the oceanic phase (Chaloupka 

 and Limpus, 2002; Chaloupka, in press). The estimate of 

 0.67 was generated for a size range from posthatchlings 

 that have left the waters directly adjacent to the nesting 



beach to subadults that begin to leave the oceanic habitats 

 at a size of 69 cm curved carapace length (Chaloupka and 

 Limpus, 2002). 



The fitted estimates for annual survival from the Heppell 

 et al. (in press) models and the Chaloupka (in press) model 

 are lower than the estimates in our study, but the size ranges 

 are different. In the Heppell et al. (in press) models and the 

 Chaloupka (in press) model, the oceanic stage includes the 

 posthatchling phase during which loggerhead sea turtles 

 migrate from nesting beaches to their oceanic habitats. We 

 could not include this early posthatchling phase in our esti- 

 mates of survival of oceanic-stage loggerhead sea turtles in 

 the waters of the Azores because many turtles in this phase 



